The present invention generally relates to a method and apparatus for reducing errors in transmission systems caused by collisions between solitons in different frequency channels, and particularly in transmission systems that utilize wavelength division multiplexing (WDM).
The above invention was supported by NSF Grant ECS-9113382 and the government has certain rights to this invention.
Collisions between solitons in different frequency channels are one of the major sources of errors in transmission systems that utilize wavelength division multiplexing (WDM). Moreover, because standard transmission lines have lumped amplification, the four-wave mixing fields from soliton collisions grow uncontrollably, adding amplitude and timing jitter to the jitter due to ideal soliton collisions. According to the present invention, these problems are addressed by using proper dispersion management, by which it is possible to significantly reduce the collision-induced timing jitter and to improve system performance even in comparison with that provided by an ideal, exponentially decreasing dispersion fiber.
Further, the present invention may significantly improve the performance of soliton communication systems with both time division multiplexing (TDM) and wavelength division multiplexing (WDM).
The present technology of WDM soliton systems uses either uniform dispersion fiber or dispersion decreasing fiber.
Various devices and methods are known pertaining to the transmission of solitons for use in telecommunications. Additionally, wave division multiplexing (WDM) is known in the field of telecommunications. Examples of such devices are discussed further hereunder.
U.S. Pat. No. 5,557,441 issued to Mollenauer discloses a soliton transmission system having plural sliding-frequency guiding filter groups to control timing jitter. The optical filters are arranged in groups whose average center frequency differs from the other groups along the length of the transmission line. The groups are arranged so as to have frequency increasing, frequency decreasing, and combinations of both, to reduce noise while permitting transmission of solitons.
U.S. Pat. No. 5,471,333 issued to Taca et al. discloses solitons, wherein wavelength dispersion is controlled by a fiber having first sections which have an average value of wavelength dispersion which is larger than the dispersion value meeting with the soliton condition, and second sections with an average value of the wavelength dispersion smaller than the dispersion value meeting with the soliton condition. The average value of the wavelength dispersion of the entire length of the optical fiber transmission line assumes a positive value.
U.S. Pat. No. 5,579,428 issued to Evans et al. was cited for teaching a single mode optical waveguide fiber using soliton signal pulses with a dispersion flattened waveguide. This reference fails to teach periodic dispersion management, nor does it address the problem of reduction of collision induced timing jitter, among other differences.
U.S. Pat. No. 5,523,874 issued to Epworth discloses an optical soliton pulse transmission system that replaces passive optical filters with active optical filters. A loop tunes the center frequency of the filter to provide a specific offset from the center frequency of the solitons.
U.S. Pat. No. 5,504,829 issued to Evans et al. discloses soliton transmission in fiber having a refractive index that monotonically decreases along the fiber.
U.S. Pat. No. 5,550,671 issued to Simpson et al. discloses Wavelength Division Multiplexed (WDM) technology. Similarly, U.S. Pat. No. 5,546,210 issued to Chraplyvy et al. discloses 4-wave mixing products with channel carriers and WDM technology.
U.S. Pat. No. 5,530,585 issued to Reid et al. discloses a dispersion shifted fiber for use in soliton optical transmission. U.S. Pat. No. 5,469,525 issued to Luther-Davies et al. discloses dark spatial soliton technology.
However, the foregoing references do not address the problem of reduction of collision induced timing Jitter, and the use of periodic dispersion management to solve this problem. Further, the foregoing references do not address the problem of improving soliton WDM transmission using periodic dispersion management.
The present invention is directed to an optical fiber and an apparatus useful in improving soliton WDM transmission using periodic dispersion management. Further, the present invention addresses the problem of reduction of collision induced timing jitter, and employs periodic dispersion management to solve this problem.
As discussed hereinabove, collisions between solitons in different frequency channels are one of the major sources of errors in transmission systems that utilize wavelength division multiplexing (WDM). Moreover, because standard transmission lines have lumped amplification, the four-wave mixing fields from soliton collisions grow uncontrollably, adding amplitude and timing jitter to the jitter due to ideal soliton collisions. The present invention, by using proper dispersion management, significantly reduces the collision-induced timing jitter and improves system performance even in comparison with that provided by an ideal, exponentially decreasing dispersion fiber.
The present invention is based on the use of alternating-sign dispersion management. A dispersion map is provided to allow significant reduction of collision-induced timing jitter in WDM systems. Such dispersion-managed fiber systems are technologically easier to construct than is a system based on dispersion-decreasing fibers. The dispersion map according to the present invention does not use any special fibers, and can be constructed from standard and dispersion-shifted fibers.
Furthermore, a particular feature of the present invention is that the dispersion map enables solitons to propagate through almost 90% of the path in normal dispersion fiber which in general does not support soliton propagation.
An object of the present invention is accordingly to improve the quality of information transmission, while at the same time improving the information capacity of the transmission fibers used.
Another object of the present invention is to improve both single and multiple channel soliton transmission.